Method of and apparatus for generating mist

ABSTRACT

A method of producing a fine mist or aerosol by means of a pressurized-gas operated mist generating head in which a foam or bubbles of liquid are supplied to the mist generating head. Apparatus for producing a mist or aerosol by means of said method.

O United States Patent 11 1 1111 3,709,433 Obergefell et al. 14 1 Jan.9, 1973 ME HO O AN APPARATUS FOR 3,527,411 9/1970 Colgan ..239/33sGENERATING MIST 3,618,856 11/1971 Sachnik ..239/s Inventors: F. Richmondl Babmgton et al. "fi Edward Kish, Cleveland FOREIGN PATENTS ORAPPLICATIONS Heights, both of Ohio 270,910 7/1964 Netherlands.....239/338 [73] Assgnee' g hdusmes Buffalo 405,389 2/1934 GreatBritain ..55/87 [22] Filed: March 25, 1971 Primary Examiner-Lloyd L.King [2 N0: Assistant Examiner-John Love Attorney--Hill, Sherman,Meroni, Gross & Simpson [52] US. Cl. ..239/8, 239/338, 239/343, 57ABSTRACT 239/366, 239/370, 239/434 1 1 [51] Int. Cl. ..B05b 7/30 A me hf pr cing a fin mi t r aero l by [58] Field of Search ..239/8, 338, 343,346, 364, means of a pressurized-gas operated mist generating 239/369,370, 366, 434; 222/193; 46/6, 7, 8; head in which a foam or bubbles ofliquid are supplied 55/87, 178 to the mist generating head. Apparatusfor producing a mist or aerosol by means of said method. [56] ReferencesCited 10 Claims, 3 Drawing Figures UNITED STATES PATENTS 2,587,8953/1952 Quinn ..46/7

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METHOD OF AND APPARATUS FOR GENERATING MIST BACKGROUND OF THE INVENTIONThere is a growing number of applications for mists or aerosols whichcomprise a dispersion of liquid in a gas medium, the liquid beingdispersed in droplets which are so small that the mist or aerosolapproaches in many respects the characteristics of natural fog.

Applications of such mists or aerosols exist in a variety of fields,including humidification, chemical treatment, coating, fuel atomization,food processing and lubrication. Applications of mists in addition tothe foregoing, however, will readily come to mind.

For convenience, the present invention will be described in the artassociation of an oil mist lubricating system,since one of the importantapplications of the invention resides in the lubrication field. It willbe apparent to those skilled in the art, however, that the presentinvention is of utility in the production of mist or aerosols for avariety of applications of which the lubrication field is onlyexemplary.

In the prior art mists or aerosols are produced by various apparatuswhich employs a stream of pressurized gas to serve as a medium forliquid particles after the gas stream has itself reduced the liquid toparticle size. One system known in the prior art relies upon theprinciples of a venturi for breaking down a stream of liquid intoextremely small and substantially uniform particles. See, for example,U.S. Pat. No. 3,491,855 of which one of the joint applicants hereof isjoint patentee.

Another known system involves the utilization of the principles ofvortex for subjecting a stream of liquid to a stream of high pressuregas with a resulting reduction of the liquid to particle size, whichparticles are carried away and dispersed within the gas. See, forexample, Hierta et al. U.S. Pat. No. 3,515,676.

Yet another method which employs pressurized gas is disclosed inBabington et al. U.S. Pat. No. 3,421,692. In this latter method a streamof liquid is deposited on a downwardly sloping smooth unconfiningsurface in which an aperture is formed. As the liquid flows downwardlyover the surface it is subjected to an internal lateral stress, themagnitude of which depends upon the extent to which the liquid is causedto film out on the surface, which in turn depends upon the adhesiveproperties of the liquid with respect to the surface and the cohesive,strength of the molecules of the liquid itself. The ability of theliquid to film out on the surface is discussed in detail in saidBabington et al. U.S. Pat. No. 3,421,692. This latter method ofproducing mist may be conveniently referred to as the wet surfacemethod, as contrasted with the venturi method disclosed in, saidObergefell et al. U.S. Pat. No. 3,491,855 and with said vortex" methoddisclosed in said Hierta et al. U.S. Pat. No. 3,515,676.

Regardless of whether the venturi method or the vortex method or the wetsurface method is employed, however, there exists the necessity forsubjecting the liquid to a stream of pressurized gas such as air or thelike and the physical structure or apparatus which performs the functionof subjecting the liquid to the pressurized stream of gas may beconveniently referred to herein as a mist generating head. It will beappreciated, therefore, that as used herein the term mist generatinghead may refer to apparatus which employs either the venturi method, thevortex method or the wet surface method of mist generation.

While all three of these known methods of producing mist aresatisfactory for the intended purpose it has been determined that theefficiency of the method and the characteristics of the mist producedthereby can be improved by virtue of the present invention. Theaforementioned result obtains regardless of whether the resulting mistis used in conjunction with a mist lubrication system, an exemplaryembodiment of which is disclosed in said Obergefell et al. U.S. Pat. No.3,491,855, or in any other aerosol or mist application.

SUMMARY OF THE INVENTION In light of the foregoing the present inventionmay be defined as a method of and apparatus for generating a mist oraerosol by prestressing the liquid before it is subjected to the effectsof the pressurized stream of gas. The liquid is prestressed bysubjecting it to a jet of gas which forms a foam of small gas-filledbubbles. The liquid which forms the enclosures of the bubbles is in theform of a thin internally stressed film. Thus when the pressurizedstream of gas medium is introduced to the bubbles of the foam the liquidfilm forming the enclosure of each bubble is atomized to becomedispersed within the gas medium and to produce mist similar to thatproduced by the venturi, vortex or wet surface methods of mistgeneration known heretofore.

The present invention is disclosed herein in the art association of awet surface method of mist generation but the principles of theinvention are of equal utility in the venturi and vortex methods of mistgeneration discussed hereinabove. For that reason said U.S. Pat. Nos.3,421,699; 3,491,855 and 3,515,676 are incorporated herein by reference.

In all three of the above methods of producing mist known heretofore thestream of pressurized air subjects the liquid to a condition of highstress, as a consequence of which the liquid is broken up into very fineparticles. By virtue of the present invention, however, the liquid isalready in the form of highly stressed film so that when it becomessubjected to the additional stress caused by the stream of pressurizedgas it is broken down into fine particles much more easily, that is,using less gas per unit of liquid. Thus if air, for example, is beingused as the gas medium the C.F.M. of air required at a predeterminedpressure for a given rate of mist production is less. Thus theefficiency of the mist generating system is increased. In addition thesize of the liquid particles are generally smaller and more uniform insize.

It is, therefore, an object of the present invention to provide animproved method of and apparatus for generating a mist or aerosol.

Another object is to increase the efficiency of a mist producing system,

Many other features, advantages and additional objects of the presentinvention will become manifest to those versed in the art upon makingreference to the detailed description which follows and the accompanyingsheet of drawing, in which preferred structural embodimentsincorporating the principles of the present invention are shown by wayof illustrative example only.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view of a mistgenerating system incorporating the principles of the present invention.

FIG. 2 is another embodiment of a mist generating system incorporatingthe principles of the present invention.

FIG. 3 is an enlarged view of a so-called wet ball which is used in theembodiments shown in FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a mistgenerating system incorporating the principles of the present invention.The embodiment shown in FIG. 1 includes a mist generating head whichincorporates the principles of the wet surface method of mist generationdiscussed hereinabove in connection with Babington et al. US. Pat. No.3,421,692 but it will be understood that the principles of the presentinvention find equal utility in other methods of generating mistincluding the venturi and vortex methods discussed hereinabove.

The mist generating apparatus shown in FIG. 1 comprises generally ahousing indicated at reference numeral including an upper portion 11 anda lower portion 12. The upper and lower portions 11 and 12 are joinedtogether by any suitable means such as threaded fasteners or the like.The upper housing portion 11 encloses various components of the systemwhereas the lower portion 12 serves primarily as a reservoir for asupply of liquid shown at 13. Since the mist generating system 10 may beadvantageously used in centralized oil mist lubrication systems theliquid 13 will be referred to herein as oil and the mist or foggenerated by the system 10 as constituting oil mist but it will beunderstood that such terms are being used herein for convenience sincethe system 10 may be utilized in generating mist from any liquid andusing any gas as the gas medium of the mist.

The system 10 may be more particularly characterized as comprising amist generating head indicated generally at reference numeral 14 which,in the embodiment illustrated, comprises a generally spherically shapedmember 16, which may be conveniently referred to as a wet ball and adelivery tube 17 formed in a block member 18 and having a discharge end19 situated in closely spaced relation to the outer surface of the wetball 16.

As will be understood by those skilled in the art, the wet ball 16 ishollow and is formed on the end of a hollow tube 20 having a tubular end21 which extends into an internal chamber 22a of a plenum 22.

Threaded into the plenum 22 in communication with the chamber 22a is aconduit 23 which may be connected to any suitable source of pressurizedgas. In the embodiment illustrated it will be assumed that the gasmedium for the oil mist is air and that an outer end 24 of the conduit23 is connected to a suitable source of pressurized air such as an aircompressor. Mounted in the conduit 23 is an air pressure gauge 26 and afilter 27. Also mounted in the conduit 23 is an adjustable pressureregulator 28 for selectively varying the pressure of the air beingsupplied to the plenum chamber 22a.

Pressurized air from the plenum chamber 22a flows through the tube 20 tothe interior of the wet ball 16 from whence it flows through a smallslit or aperture 29 formed therein.

Located in the upper housing portion 11 is a venturi chamber 30 in whichis disposed a venturi plug 31. Projecting from a generally cylindricallyshaped portion 32 of the plug 31 is a nose section 33, the forward endof which is disposed in a conical chamber 34.

Extending through a portion of the plug 31 is an axial passage 36 whichcommunicates with a radial passage 37. The passage 37 communicates withthe plenum chamber 22a through aligned passages 38 and 39.

The forward end of the passage 36 formed in the venturi plug 31converges outwardly to reduce the pressure in the chamber 30 by virtueof eduction principles, as will be appreciated by those skilled in theart. The chamber 311 communicates with the oil 13 located within thereservoir 12 through an oil supply tube 40.

In operation, a substantial portion of the air which enters the plenumchamber 22a through the conduit 24 flows through the wet ball 16 andissues from the aperture 29 as a fine jet of air. A smaller portion ofthe air flows through passages 38 and 39 into the venturi plug 31, andas it issues from the passage 36 it provides a reduced pressure in thechamber 30 by virtue of which a supply of oil is drawn up through thesupply tube 40.

The oil is subjected to the stream of air issuing from the venturi plug31 to form an oil foam in the discharge passage 41' communicating withthe conical chamber 34. The oil foam is comprised of extremely smallbubbles which are substantially uniform in size. The foam is conductedthrough the passage 41 into a supply chamber 42 which communicates withthe passage 17 located adjacent the wet ball 16.

An upper end 19a of the passage 17 is formed in a protuberance 43 whichextends above a top wall 44 of the block member 18. This arrangementensures that the foam in the chamber 42 must rise above the end 19a ofthe passage 17 before it will discharge through the passage 17 down tothe surface of the wet ball 16.

The bubbles which comprise the oil foam as it flows over the outersurface of the wet ball 16 are enclosed respectively by a film of oil.This film, of course, is under an internal stress which results from thepressure of the air within the bubble.

Referring to FIG. 3, the oil foam flows downwardly over the outersurface of the wet ball 16 in a relatively thin layer and a substantialportion thereof drips back into the reservoir 12 from the bottom of thewet ball 16. As it flows across the wet ball 16, however, the film ofoil surrounding each bubble in contact with the surface of the wet ballis subjected to an additional internal lateral stress, the magnitude ofwhich depends upon the adhesive properties of the oil vis-a-vis thesurface of the wet ball 16 and, of course, the cohesive strength of themolecules of the oil itself.

FIG. 3 illustrates somewhat diagrammatically or pictorially theappearance of a layer of oil foam, indicated at reference numeral 46 asit flows from the passage 17 over the surface of the wet ball 16.Assuming that the adhesive properties of the surface of the wet ball 16relative to the oil which comprises the foam 46 is greater than thecohesive strength between the molecules of the oil itself so that thesurface of the wet ball 16 is wettable relative to the oil, the oilwithin the bubbles of the foam 46 will tend to film out or spread evenfurther over the surface of the wet ball 16. This additional filming outor spreading produces additional internal stresses in the liquid oilfilm and particularly as it approaches and passes over the aperture 29.As the jet of gas (air, in the illustrated embodiment) engages the filmof oil which is prestressed first of all because of the formation of thebubbles and secondly because of the wetting action of the surface of thewet ball 16, the film of oil surrounding the individual bubbles isbroken down into minute particles and dispersed within and carried bythe gas to produce a fog or mist as indicated at reference numeral d7.

Passages 48-50 communicate with a chamber 5 ll in which the mistgenerating head 14 is disposed to direct the oil mist or fog 47 issuingfrom the head lid to an outlet 52 formed in the upper housing portion M,and thence to one or more points of utilization, such as the severalbearings of a multi-bearing machine.

It is noted that the present invention differs from the mist generatingsystems known heretofore in that the liquid or oil is additionallyprestressed before it is subjected to the impact of the stream or jet ofpressurized gas by virtue of the fact that it is in the form of bubblesor foam when subjected to the gas or air stream. In the systems knownheretofore the liquid which is to be atomized is either in the form of asolid stream of liquid as it is introduced to the stream or jet ofpressurized air or, as is shown in said Babington et al. U.S. Pat. No.3,421,692, is prestressed in the form of a film by spreading the liquidover a wettable surface before it is subjected to the stream ofpressurized air.

In the present invention the liquid such as oil is prestressed in theform of a film before it is subjected to the stream of pressurized gasby means of aeration principles whereby the liquid, before it issubjected to the pressurized gas stream, is converted to film form. Thefilm encloses the gas such as air and is subjected to internal lateralstress which is commensurate with the size of the bubble or area of thefilm and the pressure of the gas within the bubble.

It has been determined that the mist generating head 14 as well as thoseof the venturi and vortex types discussed hereinabove are much moreefficient in producing mist and in producing a more uniform mist whenthe liquid forming the mist is prestressed in the form of a film foam.The liquid is apparently broken up by the pressurized gas into minuteparticles much more easily and with much greater effectiveness as aconsequence of the prestressed condition of the liquid foam as it comesin contact with the jet of pressurized air.

FIG. 2 illustrates a mist generating system which is similar to thesystem shown in FIG. 1 but which differs in several respects. Because ofthe similarity of the two systems, however, parts shown in FIG. 2 whichcorrespond to those shown in FIG. 1 will be. identified with similarreference characters.

In the embodiment shown in FIG. 2 the wet ball 16 is supplied withpressurized air from an electric motor driven self contained aircompressor indicated generally at reference numeral 53. The compressorcomprises a piston 54 housedin a cylinder 56 formed in a housing portion57 adjacent the upper housing portion it. The piston 54 is connected bymeans of a rack 58 to an eccentric shaft 59 extending from a drivemember 60' mounted on a motor shaft 61. The shaft 61 serves as anarmature shaft for an electric motor indicated at reference numeral 62as will be appreciated by those skilled in the art.

One end 63 of the cylinder 56 disposed on the leftward side of thepiston 54 is viewed in FIG. 2, communicates with ambient air through anaperture 64 formed in an end wall 66 of the housing portion57. Anopposite end 67 communicates with a passage 68 which in turncommunicates with the plenum chamber 22a through a conduit 69 and to thereservoir 12 through a conduit 79.

A spring biased check valve 71 is mounted in the conduit 69 and anothercheck valve 72 is mounted in the conduit 70. The valve 71 is biased to aclosed position during the suction stroke of the piston 54, whereas thevalve '72 is biased to a closed position during the discharge stroke ofthe piston. Consequently, the air which is used to provide thepressurized stream of air issuing from the aperture 29 of the: wet ball16 is drawn up from the reservoir 12, above the level of oil 13 therein,and into the wet ball as a. consequence of the pumping action of thepiston 54.

In the embodiments of FIGS. 1 and 3 a conduit indicated at referencenumeral 51a communicates the passage 41, which is on the downstream sideof the venturi plug 31 and is filled with oil foam, with the chamber 51in which the wet ball 16 is disposed, thus maintaining the pressure inthe passage 41 essentially at atmospheric pressure. This, of course,precludes any substantial buildup in pressure in the foam. Any foampassing through the passage 51a is discharged through an outlet 51b intothe chamber 51 and thence back into the reservoir 12.

It will be appreciated that only the oil foam which flows over theaperture 29 is broken down into mist particles. The remaining foammerely falls back into the reservoir 12. However, the quantitative ratioof liquid pumped to the mist generating head to that which drops back tothe reservoir is considerably lower where the liquid is aerated orfoamed in accordance with the principles of the present invention ascontrasted with the solid stream of liquid disclosed in prior art mistgenerating systems.

Although minor modifications might be suggested by those versed in theart, it should be understood that we wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably comewithin the scope of our contribution to the art.

What we claim is:

l. A method of producing a mist or aerosol comprising the steps ofdirecting a stream of pressurized gas flhltii-igh a pressurized gasoperated mist generating aerating a supply of liquid to form a foamcomprising small gas-filled bubbles of the liquid, and

introducing a stream of said foam into the stream of pressurized gaswhereby the bubbles are broken by and minute particles of the liquid areatomized and dispersed in the gas stream. 1

2. A. method of producing a mist or aerosol by dispersing a liquid intoagaseous medium comprising the steps of a aerating a quantity of theliquid to form a foam comprising small gas-filled bubbles of the liquidwhereby the liquid film which surrounds the gas in the bubbles is underan internal lateral stress,

directing a stream of said foam over a smooth unconfining surface andacross an aperture formed in the surface to further internally laterallystress the liquid film as it approaches and passes over the aperture,and supplying under pressure and through said aperture and toward thestream of bubbles passing across the aperture a gas which serves as thegas medium of the mist,

said gas medium further stressing the liquid film and reducing same tominute particles ofliquid carried away from said aperture by the gasmedium in the form of a fine mist.

3. The method as defined in claim 2 wherein said smooth unconfinedsurface is convexly shaped.

4, A method of producing a fog comprising the steps of providing astream of liquid-gas foam comprising small gas-filled liquid bubbles inwhich the liquid surrounding the gas is in the form of thin internallylaterally stressed film, and directing into said stream of bubbles astream of gas under pressure to further stress and rupture the liquidfilm to produce minute particles of liquid carried in the gas as a finemist.

5. Apparatus for producing a mist comprising a pressurized gas operatedmist generating head,

means for directing a stream of pressurized gas through said mistgenerating head,

means for aerating a supply of liquid to form small gas-filled bubblesof the liquid, and

means for introducing a stream of said bubbles into the stream ofpressurized gas whereby the bubbles are broken by and minute particlesof the liquid are atomized and dispersed in the gas stream.

6. Apparatus for producing a mist or aerosol comprising means forconfining a quantity of liquid,

means for introducing a stream of gas into the liquid so confined toform a foam comprising small gasfilled bubbles of liquid whereby theliquid which surrounds the gas in the bubbles is in the form of a thininternally stressed film,

means forming a smooth unconfining surface having an aperture formedtherein,

means for directing a stream of said foam over said surface and acrosssaid aperture to further internally stress the liquid film as itapproaches and passes over said aperture, and

means for supplying a gas medium under pressure through said apertureand toward the stream of foam passing across the aperture, whereby theliquid film is further stressed and reduced to minute particles whichare carried away from said aperture in the form of a fine mist by thegas medium.

7. The invention as defined in claim 6 wherein a portion of said smoothunconfining surface is convexly shaped. j

8. Apparatus for producing a liquid-gas mist of aerosol comprising meansforming a reservoir for the liquid to be used in producing the mist,means forming a smooth downwardly sloping unconfining surface having anapgrture formed therein, I

mean or producing a stream of pressurized gas issuing, from saidaperture, and

means for producing a foam comprising gas-filled bubbles of said liquidand for directing a stream of said foam onto said surface above saidaperture for flowing gravitationally downwardly across said aperturetoform a fine mist with said gas issuing from said aperture.

9. The invention as defined in claim 8 wherein said foam producing meanscomprises means forming a gasoperated venturi for drawing liquid fromreservoir into said venturi means to generate said foam.

10. The invention as defined in claim 9 wherein said foam producingmeans further comprises an electric motor operated air compressor forsupplying pressurized air to said venturi means.

t I I t

1. A method of producing a mist or aerosol comprising the steps ofdirecting a stream of pressurized gas through a pressurized gas operatedmist generating head, aerating a supply of liquid to form a foamcomprising small gasfilled bubbles of the liquid, and introducing astream of said foam into the stream of pressurized gas whereby thebubbles are broken by and minute particles of the liquid are atomizedand dispersed in the gas stream.
 2. A method of producing a mist oraerosol by dispersing a liquid into a gaseous medium comprising thesteps of aerating a quantity of the liquid to form a foam comprisingsmall gas-filled bubbles of the liquid whereby the liquid film whichsurrounds the gas in the bubbles is under an internal lateral stress,directing a stream of said foam over a smooth unconfining surface andacross an aperture formed in the surface to further internally laterallystress the liquid film as it approaches and passes over the aperture,and supplying under pressure and through said aperture and toward thestream of bubbles passing across the aperture a gas which serves as thegas medium of the mist, said gas medium further stressing the liquidfilm and reducing same to minute particles of liquid carried away fromsaid aperture by the gas medium in the form of a fine mist.
 3. Themethod as defined in claim 2 wherein said smooth unconfined surface isconvexly shaped.
 4. A method of producing a fog comprising the steps ofproviding a stream of liquid-gas foam comprising small gas-filled liquidbubbles in which the liquid surrounding the gas is in the form of thininternally laterally stressed film, and directing into said stream ofbubbles a stream of gas under pressure to further stress and rupture theliquid film to produce minute particles of liquid carried in the gas asa fine mist.
 5. Apparatus for producing a mist comprising a pressurizedgas operated mist generating head, means for directing a stream ofpressurized gas through said mist generating head, means for aerating asupply of liquid to form small gas-filled bubbles of the liquid, andmeans for introducing a stream of said bubbles into the stream ofpressurized gas whereby the bubbles are broken by and minute particlesof the liquid are atomized and dispersed in the gas stream.
 6. Apparatusfor producing a mist or aerosol comprising means for confining aquantity of liquid, means for introducing a stream of gas into theliquid so confined to form a foam comprising small gas-filled bubbles ofliquid whereby the liquid which surrounds the gas in the bubbles is inthe form of a thin internally stressed film, means forming a smoothunconfining surface having an aperture formed therein, means fordirecting a stream of said foam over said surface and across saidaperture to further internally stress the liquid film as it approachesand passes over said aperture, and means for supplying a gas mediumunder pressure through said aperture and toward the stream of foampassing across the aperture, whereby the liquid film is further stressedand reduced to minute particles which are carried away from saidaperture in the form of a fine mist by the gas medium.
 7. The inventionas defined in claim 6 wherein a portion of said smooth unconfiningsurface is convexly shaped.
 8. Apparatus for producing a liquid-gas mistof aerosol comprising means forming a reservoir for the liquid to beused in producing the mist, means forming a smooth downwardly slopingunconfining surface having an aperture formed therein, means forproducing a stream of pressurized gas issuing frOm said aperture, andmeans for producing a foam comprising gas-filled bubbles of said liquidand for directing a stream of said foam onto said surface above saidaperture for flowing gravitationally downwardly across said aperture toform a fine mist with said gas issuing from said aperture.
 9. Theinvention as defined in claim 8 wherein said foam producing meanscomprises means forming a gas-operated venturi for drawing liquid fromreservoir into said venturi means to generate said foam.
 10. Theinvention as defined in claim 9 wherein said foam producing meansfurther comprises an electric motor operated air compressor forsupplying pressurized air to said venturi means.